Electron multiplier tube



Nov. 12,1940? 4 a) B. BANKS 2,221,070

ELECTRON MuETiPLIER TUBE Filed Oct. '7, 1938 //v ur ourpur INVENTOR a.5. BANK-S ATTORNEY Patented Nov. 12, 1940 2,221,070 ELECTRON MULTIPLIERTUBE.

George Baldwin Banks, Billerioay, England, as i signor to RadioCorporation of America, a cor poration of Delaware Application October'7, 1938, Serial No. 233,702

In Great Britain December 1, 1937, I l

2 Claims. (01. 250-) This invention relates to electron multiplierdischarge tubes, 1. 'e. to discharge tubes of the type wherein aninitial electron stream is multiplied as to its electron content one ormore times by secondary emission effects. The invention has for its mainobject to provide a grid controlled electron multiplier tube capable ofgiving very high gain without instability.

According to this invention an electron multiplier discharge tubecomprises within an evacuated envelope, a pair of output electrodes, oneor more secondary emitting or multiplier electrodes, a primary electronsource, two or more field electrodes, one opposite each multiplierelectrode and one opposite the said primary electron source, an electronimpermeable barrier situated between the field electrodes and themultiplier electrodes and so positioned and of such extent aseffectively to separate the series of paths which proceed from theprimary electron source (via the multiplier electrode or electrodes) toone output electrode from the similar series of paths terminating at theother output electrode, and independent means for controlling theelectron streams on the two sides of said barrier.

The invention is illustrated in the accompanying drawing in which:

Figure 1 shows, in schematic perspective the electrode system of oneembodiment of the invention and Figure 2 is a diagram showing theembodiment of Figure 1 connected in a suitable operating circuit.

Referring to the drawing there is provided within an evacuated envelopea seriesfo-r example two-of fiat plate-like co-planar secondary emissivemultiplier electrodes SPI, SP2 of any form known per se. Opposite eachmultiplier electrode is a field electrode Pl, P2. A cathode C, forexample an indirectly heated thermionic cathode is fitted to one side ofthe series of multiplier electrodes SPI, SP2 approximately co-planartherewith. There are two control electrodes GI, G2 each in the form of aslotted plate fitted over one or the other half of the length of thecathode 0, these control electrodes being insulated from one another andbeing also co-planar with the multiplier electrodes. The slots in thecontrol electrodes are positioned to allow electrons to emerge, underthe control of said control electrodes, and proceed in roughly circularor cycloidal paths to the first multiplier electrode SPl. Grid wires areshown fitted across the slots in the control electrodes GI, G2. A fieldelectrode P, co-planar with the other field electrodes Pl, P2 is, positioned opposite the cathode and control ,electrode structure. A mica orother suitable barrier B is positioned between the two planes ofelectrodes perpendicularly to said right angles to the direction oflength of cathode, this barrier being central so as to divide theslablike space between the two said planes into two equal parts.Situated between these twoplanes and at right angles thereto are twoco-planar output electrodes Al, A2, these electrodes being at the end ofthe slab remote from the cathode and one each side of the barrier.

A tube as above described is for and is primarily intended for use inpull operating circuit. For example as shown in Figure 2 the two controlelectrodes GI, G2 may be connected to the two ends of a center-tappedpush-pull input transformer secondary IS and the two output electrodesmay be similarly connected to the two ends of a center tapped pushpulloutput transformer primary OP. In use inplanes and extends atadmirablysuited a pushcreasingly positive potentials are applied to the field,multiplier and output electrodes (increasing in the direction of theoutput electrodes) and a magnetic field is applied to thread the fieldelectrode-multiplier electrode space in a direction (represented by thearrow in Figure 1) at right angles to the cathode-output electrodedirection, the lines of force running substantially parallel to thefield and multiplier electrode planes.

It will be seen that with the tube above described both branches of apush-pull system are provided in the one envelope but the secondaryemission stages are common to both branches, i. e. the system isbifurcated only as regards the control electrodes, the output electrodesand, of course, the electron paths. Accordingly great freedom fromfeed-back and good stability are obtained. The current taken from anymultiplier electrode remains-when the tube is used in a push-pullcircuit-sensibly constant, for the control electrode potentials beingout of phase a current increase in one branch is ac-, companied by anequal decrease in the other. Accordingly a multiplier electrode when fedfor example from a potentiometer, remains at substantially'constantpotential this again increasing stability.

Finally, by employing a high value of negative bias on the controlelectrodes it is possible to limit the steady direct current to a verysmall value and thus obtain so-called quiescent pushpull operation.Consequently very high gains,

not subjected to the at present usual close limitation by heating efiectof the steady current on the multiplier electrodes, is obtainable.

Having now particularly described and ascertained the nature of our saidinvention and in What manner the same is to be performed, We declarethat what we claim is:

1. Anelectron discharge tube of the multiplier type comprising a sourceof primary electrons, a plurality of longitudinally spaced grids forcontrolling the intensity of the flow of electrons from said source toproduce a plurality of separately modulated primary electron streams, asingle planar accelerating electrode common to all of the electronstreams, said accelerating electrode being mounted in a predeterminedplane and adapted to attract the electrons constituting the electronstreams, a single planar secondary electron emissive surface positionedin the path of the primary electron streams to produce separatesecondary electron streams, and a plurality of electron collector anodesfor independently whereby two independently modulated streams ofelectrons may be produced, a pair of co-planar electron acceleratingelectrodes for the electron streams, a secondary electron emissivesurface positioned in the path of and common to both streams ofelectrons to produce separate secondary electron streams, and acollector anode for each stream of secondary electrons, the secondaryelectron emissive surface and the source of primary electrons beingpositioned in a plane substantially parallel to the plane of theacceler- 20 ating electrodes.

GEORGE BALDWIN BANKS.

